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CQC2T scientists, led by Prof Michelle Simmons, have achieved a new milestone in their approach to creating a quantum computer chip in silicon, demonstrating the ability to tune the control frequency of a qubit by engineering its atomic configuration.

The team from UNSW Sydney successfully implemented an atomic engineering strategy for individually addressing closely spaced spin qubits in silicon. The scientists created engineered phosphorus molecules with different separations between the atoms within the molecule allowing for families of qubits with different control frequencies. Each molecule could then be operated individually by selecting the frequency that controlled its electron spin.

“The ability to engineer the number of atoms within the qubits provides a way of selectively addressing one qubit from another, resulting in lower error rates even though they are so closely spaced,” says Professor Simmons. “These results highlight the ongoing advantages of atomic qubits in silicon.”

Tuning in and individually controlling qubits within a 2 qubit system is a precursor to demonstrating the entangled states that are necessary for a quantum computer to function and carry out complex calculations.

“We can tune into this or that molecule – a bit like tuning in to different radio stations,” says Sam Hile, lead co-author of the paper and Research Fellow at UNSW. “It creates a built-in address which will provide significant benefits for building a silicon quantum computer.”

Centre researchers set world record simulating quantum power

CQC2T scientists from the University of Melbourne have set a world record in simulating quantum power on a classical computer, a key step in becoming 'quantum-ready' ahead of when actual quantum computers are scaled up in size. Deputy Director of CQC2T, Professor Lloyd Hollenberg and team members Dr Charles Hill and lead author Masters student Aidan Dang, simulated the output of a 60-qubit quantum computer, which in general would require up to 18,000 petabytes, or more than a billion laptops, to describe – capabilities well beyond the largest supercomputer.

A representation of quantum computing in action showing the “forest” of differing probabilities that the machine uses to more efficiently guide it towards the answer to a problem. The above example is a simulation of a quantum computer finding the prime factors of a number using Shor’s Algorithm.Picture: Matthew Davis, Gregory White and Aidan Dang